Heart failure refers to the inability of the heart to keep up with the functional demands made upon it. Congestive heart failure refers to an inability of the heart to pump an adequate amount of blood to the body tissues. In other words, congestive heart failure is characterized by inadequate cardiac output.
Because the heart is unable to pump an adequate amount of blood, blood returning to the heart becomes congested in the venous and pulmonary system. A patient with congestive heart failure may be unable to pump enough blood forward to provide an adequate flow of blood to his kidneys, for example, causing him to retain excess water and salt. His heart may also be unable to handle the blood returning from his pulmonary system, resulting in a damming of the blood in the lungs and increasing his risk of developing pulmonary edema.
Symptoms experienced by a patient with congestive heart failure may include breathing difficulty caused by pulmonary edema, swelling, particularly of the lower extremities, fatigue, difficulty concentrating, dizziness, and fainting. During periods where a patient with congestive heart failure is experiencing severe symptoms, breathing difficulty may be such that the patient cannot lie down to sleep, and the patient may feel as though they are suffocating.
Patients with congestive heart failure may be treated with pharmacological therapies to increase cardiac output. Some patients with congestive heart failure benefit from an implanted pacemaker that increases cardiac output by increasing the heart rate, or synchronizing the contraction of the ventricles of such patients. When a patient experiences severe symptoms, the patient may be admitted to hospital or clinic, and receive supplemental pharmacological therapy to alleviate the symptoms. This situation may be very costly because of the hospital stay, nursing costs, patient transportation costs, and so forth.
Another malady that may affect the cardiac output of a patient's heart is a tachyarrhythmia, such as ventricular tachycardia or ventricular fibrillation. Ventricular fibrillation is particularly life threatening because activity within the ventricles of the heart becomes so uncoordinated that virtually no pumping of blood takes place. With a brain deprived of oxygenated blood, the patient loses consciousness within a matter of seconds, and will die within minutes if not treated.
An electrical shock delivered to a fibrillating heart may repolarize the heart and cause it to reestablish a normal sinus rhythm. Patients who have experienced one or more episodes of ventricular fibrillation may receive an implanted pacemaker cardioverter-defibrillator (PCD). The PCD may detect the occurrence of ventricular fibrillation, charge an energy storage circuit, and deliver a defibrillation shock to the patient using the stored energy.
However, the charge time for a PCD typically ranges from seven to ten seconds when the PCD is new, but may be as long as twenty seconds as the energy storage circuit and power source age. Therefore, despite the implantation of a PCD, patients who have ventricular fibrillation episodes often collapse before a defibrillation shock is delivered. Because of the risk of collapse, some patients must modify their lifestyles by, for example, refraining from driving, riding a bicycle, swimming unattended, holding a grandchild, and the like. Further, falling from hemodynamic collapse frequently results in orthopedic injury, particularly in a patient of advanced age.